We can (again) check for updates and, if an update is available, send
the user to the site to download them.

The old format (a .json specifying a version number and download URL)
was kept. The address for this file is now specified in the settings.

We can (again) check for updates and, if an update is available, send
the user to the site to download them.

The old format (a .json specifying a version number and download URL)
was kept. The address for this file is now specified in the settings.

This removes a few instances of deleting a scene twice, or accessing
elements of a scene after they've been deleted.

Previously, the application would crash upon exiting if the scene was
empty but had been modified (e.g if an object was placed on the board
then deleted, then the application closed)

Several issues remain with multi-screen mode on Linux. The behavior is
inconsistent from one desktop evironment to the next, making it hard to
work around these problems. Among the known issues at this stage:

On Ubuntu 14.04, a call to QWidget::setGeometry requires the widget to
be hidden on KDE, but visible on MATE, for the geometry changes to take
effect.
Despite the widget's geometry being updated by this call, the windows
aren't necessarily moved. Meaning that the control and display widgets
will tend to be displayed on the same monitor, even though their
positions are correctly set to different areas on the extended screen.

In the current state, this behavior is observed on MATE. Unity works
fine and KDE only has transient positioning issues (for example,
swapping control and display windows in multi-screen mode leads to both
windows being placed on the same monitor, until multi-screen mode is
turned off then on again).

# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
# On branch dev
# Your branch is ahead of 'origin/dev' by 29 commits.
#   (use "git push" to publish your local commits)
#
# Changes to be committed:
#	modified:   src/core/UBApplicationController.cpp
#	modified:   src/core/UBDisplayManager.cpp
#	modified:   src/core/UBDisplayManager.h
#
# Changes not staged for commit:
#	modified:   release_scripts/linux/build.sh
#	modified:   release_scripts/linux/package.sh
#
# Untracked files:
#	release_scripts/linux/generateDependencies.sh
#

Fix for window being placed badly on the screen when returning to board mode from desktop mode on some environments

This reverts commit 4aa0ee61.

When the time comes to merge dev into master (for real), the
following may be useful:
https://metlos.wordpress.com/2012/01/13/
git-merging-after-a-revert/

("http://get.openboard.org/update.json").
=> the url do not exists.

Application compiles and runs, with some caveats. Full list of changes:

- minor changes related to Qt4->Qt5 API differences

- Replaced calls to Carbon framework by Cocoa

- Removed registering of AE event handler. Seems to be done
automatically in Qt5.

- temporarily removed Podcast functionality, pending (presumably)
complete re-write due to Quicktime being obsolete in newer OS X
versions.

- Created OBCocoa namespace, and associated files src/core/OBCocoa.h/.mm, to
handle OS X - specific system calls. Currently used only by
UBApplication, but can in the future provide a useful interface between
the cocoa framework and OB, to avoid having too much OSX-specific code
in various files

Q_WS_MACX -> Q_OS_OSX
Q_WS_MAC -> Q_OS_OSX
Q_WS_WIN -> Q_OS_WIN
Q_WS_X11 -> Q_OS_LINUX